This invention relates to the field of integrated circuit fabrication. More particularly, this invention relates to a method of determining and compensating for exposure and etch induced inconsistencies during integrated circuit manufacturing processes.
Integrated circuit fabrication techniques typically use a mask to project patterns of electromagnetic radiation onto a layer of photoresist on a substrate. The electromagnetic radiation is typically of a wavelength in the ultra violet band, but may be from another portion of the spectrum. The density of the features defined by projecting the mask pattern onto the photoresist tends to be limited by various distorting characteristics of the mask, the radiation, and the photoresist, such as diffraction, which tend to vary the pattern as it is projected from the mask onto the substrate.
Various techniques have been developed to counteract the effects of these distorting characteristics. One such technique, optical proximity correction, provides distortion compensating patterns throughout the mask. The distortion compensating patterns compensate for the distorting characteristics described above, thereby resulting in the projection of a correct pattern onto the photoresist. By using such optical proximity correction techniques, projected features on the substrate can be smaller and more densely packed.
As implied above, the patterns projected onto the photoresist are subsequently used to mask an underlying layer during an etch step. Unfortunately, additional distortion to the shape of the desired feature occurs during the etch step. This situation tends to further limit the feature density of the integrated circuit, in a manner similar to that as mentioned above. Optical proximity correction techniques, such as described above, tend to not correct the distortion of the desired pattern that occurs during the etch step.
What is needed, therefore, is a system for accounting for the differences between a pattern on a mask and the etched pattern in a layer that is eventually produced by use of the mask.
The above and other needs are met by a method for adjusting preliminary feature position characteristics of a preliminary mask pattern on a mask to produce a desired etch pattern on a substrate having desired feature position characteristics. The feature positions are adjusted by calculating adjustment distances based on the numbers in a table. Prior to adjusting preliminary mask features, the table is computed, based on measurements made of a test pattern etched on a substrate which was previously manufactured by exposing a test mask, or in other words, a mask with the test pattern on it. The feature position characteristics of the test pattern on the test mask are measured at locations on the test mask corresponding to a first set of given locations, to produce a first set of position data.
Test feature position characteristics of a test etch pattern on the substrate are measured at locations on the substrate corresponding to the first set of given locations, to produce a second set of position data. The test etch pattern is produced through use of the test mask pattern. A first database of differences between pairs of the first set of position data and the second set of position data is computed, where the pairs are associated by similar locations in the first set of given locations.
A third set of position data corresponding to the first set of given locations from a target contour of an aerial simulation of anticipated intensity values is generated from the test mask pattern on the test mask. A second database of differences between pairs of the first set of position data and the third set of position data is computed, where the pairs are associated by similar locations in the first set of given locations.
A transformation is generated, where inputs to the transformation correspond to the third set of position data and outputs from the transformation correspond with values of the first database and the second database.
The feature position characteristics of the preliminary pattern on the preliminary mask are measured at locations on the preliminary mask corresponding to a second set of given locations, to produce a fourth set of position data. This fourth set is iteratively adjusted and input to the transformation until the output of the transformation produces adjustment values for producing the desired etch pattern. The preliminary feature position characteristics of the preliminary mask pattern of the mask are adjusted by the adjustment values to produce a compensated mask pattern that produces the desired etch pattern on the substrate having the desired feature position characteristics.
In this manner, the discrepancies between a test pattern in a mask and the test pattern as etched into a substrate can be used to set a correlation, or in other words the transformation, that can be used with other mask patterns to adjust the mask pattern so as to produce etched features in the substrate that have the desired feature position characteristics. In other words, the transformation can be used with a conventional optical proximity correction program calibrated to the target contour of the aerial image of any mask pattern to produce adjustments to the mask pattern that will tend to produce the desired pattern in the etched substrate.